Mind Matters News is pleased to offer a new series, “Monday Micro Softies,” from our director, Robert J. Marks, a series of puzzles that illustrate the ways of thinking needed in the computer industry today. – Eds.

This new Micro Softy is a puzzle based on proper ways to add numbers. (After this, I’ll give the solution to Micro Softy 5 from last Monday):

Claude noticed his son Clay adding three numbers: 2.2, 4.1 and 2.0. Clay’s answer was 9.0. Claude was about to point out the bad addition, when his son abruptly pushed back from the table, grabbed the sheet of paper he was writing on, put on his autumn coat and baseball cap, grabbed an apple for later, and sprinted out the door. Clay suddenly realized that his son had not made a mistake and that the addition was right. What did Clay realize? We’ll give the answer here next Monday.

Solution to Micro Softy 5: Claude and Chloe’s two kids

Claude and Chloe have two children. We’ve met one of them, Clay. What’s the probability the Claude’s other child is also a boy?

It feels like the answer should be 50–50, but it isn’t. The answer is one out of three or 1/3. Here’s why. For two children, here’s a list of all possibilities, listing the younger child first. G=girl and B=boy so GB means the girl is the younger of the two children.

● GG
● GB
● BG
● BB

Each combination has the same probability, that is, one chance out of four or 1/4. We already know that one of Claude’s children is a boy. So that rules out the GG possibility.

That leaves:

● GB
● BG
● BB

Each of these combinations has the same probability — namely one chance out of three or 1/3. Only one is BB so the chance that Claude’s other child is a boy is one out of three or 1/3. The chance that the other child is a girl is 2/3.

The answer would be different if Claude had introduced his son as his younger child. Then the possibilities would be:

● BG
● BB

The chance that Claude’s older child is a boy is then one half or 1/2. Not knowing whether the son is the younger or the older child makes a difference.

Here are the Micro Softies from earlier Mondays, to date. The answer to one Monday’s puzzle is always given the next Monday:

Monday Micro Softy 1: Microsoft: What did you need to work there in the early days? They asked questions that were not about the details of computer technology. The questions made you think. Hard. For example, they would ask questions like, why are manhole covers round? Also, here’s the Round Trip puzzle.

Monday Micro Softy 2: The Dead Presidents’ Club The answer to Monday Micro Softy 1: The Round Trip puzzle is here too. Today’s puzzle: How would a girl who knew nothing of American history immediately know the name of at least one of three early Presidents who died on July 4?

Monday Micro Softy 3: The Wolverton Mountain Puzzle Here’s the answer to Dead President’s Club as well — and smart STEM people often DON’T get that one right. Today’s brain teaser is in honor of Claude King, Clifton Clowers, and Wolverton Mountain. It’s not high tech but it will surely test your thinking abilities.

Monday Micro Softy 4: Claude King bests Clifton Clowers Clowers offers Claude two slips of paper to choose from on a blind choice: marriage or death… Claude’s sweetheart Chloe warns him that, in reality, both slips say “death.” He says never mind. So how did he escape death and marry her?

Monday Micro Softy 5: The puzzle of Claude and Chloe’s two kids Puzzle: We learn that one of Claude and Chloe’s two children is a boy. With a 50–50 ratio, what chance is there that the other child is a boy too? Also, here’s the answer to the puzzle of how, twelve years earlier, Claude escaped the trap Clifton Clowers set for him, so he could marry Chloe.